A low-pressure casting device typically includes a holding furnace for storing molten metal, a mold having a cavity and a stalk that communicates the holding furnace with a cavity, which is used for molding a casting by increasing the pressure in the holding furnace to supply the molten metal to the cavity through the stalk and allowing the molten metal to solidify.
A casting device is disclosed in JP 2003-251453A, which includes a molten metal passage for supplying molten metal to a cavity, having a circular cross section perpendicular to the longitudinal direction.
In the above-described device of JP 2003-251453A, it is difficult to supply molten metal to a wide area in a cavity since the molten metal passage has a circular cross section. Due to such poor delivery (running property), it has been difficult to produce a product having a complex shape or a thin product in which molten metal is rapidly cooled.
In order to improve the delivery, a flat fan gate has been provided in a sprue to supply molten metal to a wide area.
However, when the cross-sectional shape of the molten metal passage greatly changes at the connection part between the sprue and the fan gate, the change of the flow rate of the molten metal causes ruffle in the molten metal surface, which may produce an oxide in the new surface of the molten metal and result in the degraded quality of molded products.
In particular, since increasing the supply rate of the molten metal is likely to cause large ruffle, it is difficult to achieve both reduction in supply time of the molten metal and reduction in oxide production.
In order to improve the delivery while preventing ruffle of the molten metal, one possible measure is to flatten the entire sprue while keeping the cross-sectional shape of the sprue. However, the entirely flat sprue makes it difficult to adjust the solidification time of molten metal according to the size and shape of molded products. As a result, clogging of the sprue is more likely to occur, in which a molded product cannot be released from the sprue.
The present invention has been made in view of such problems with the prior art, and an object thereof is to provide a sprue for a low-pressure casting device which enables reduction of the cycle time and also prevents oxidation of molten metal and which hereby enables efficient production of high-quality molded products, and a low-pressure casting device with the sprue.